Righting Reflex] in the Cat During Weightlessness

I THE JOURNAL OF I AVIATIONMEDICINE O&hl Publication of the Aero Medical Association I 1 VOLUME 28 AUGUST, 1957 NUMBER 4 The Labyrinthine Posture Reflex (Righting Reflex] in the Cat during Weightlessness BY SIEGFRIEDJ. GERATHEWOHL,PH.D., AND MAJORHERBERT D. STALLINGS,USAF LTHOUGH it is generally ac- inner ear known as otolith organs. cepted that linear acceleration They are located in the utricle and is the physical stimulus for the the saccule which are filmled with endo- otolith organ, its function during per- lymph and contain the very special- iods of increased and decreased grav- ized structure of macula and otoliths. ity has not been ~larified.~,~J~In 1952, The otolith apparatus consists of a SlaterlG discussed the probable re- plaque of hair cells covered with a sponse of the otoliths to the weightless mucus layer, which carries a large condition by drawing some tentative number of very small particles of cal- conclusion from morphologic data and cium carbonate, the so-called otoliths. electrophysiologic experiments made When the head is in an upright posi- by Adrian1 and Lowensteing, and by tion, the macula of the utricle lies ap- Lowenstein and Raberts.lo The experi- proximately in a horizontal plane, that ments in this report deal with the of the saccule in a vertical plane. The otolith functions of the cat. The find- planes of the two saecular maculas ings are thought to throw some light form an angle opening forward and on the vestibular processes during sub- downward. gravity and zero-gravity. The probable response of this organ The means of sensing the effect of to weightlessness has been discussed gravity, which is actually a linear ac- elsewhere.6+ Because of their physical celerative force, is provided by a set characteristics, the otoliths are "gravi- of mechanically affected organs of the receptors." They can move within the macula under the pull of their own From the U. S. Air Force School of weight, or in response to accelerative Aviation Medicine, Randolph Air Force Base, Texas. forces and their inertial effects. This Presented on May 8, 1957 at the 28th movement bends or pulls, or shears annual meeting of the Aero Medical As- sociation, Denver, Colora'do. the epithelial hairs, thus distorting the 345 POSTURE REFLEX--GERATHEWOI-IL AND STALLINGS sensory cells and producing a stimulus. gravity has an essential effect upon Depending upon the position of the animal life. This effect is very diffi- head in the state of rest, the end cult to assess but relatively easy to org'ans of the utricle and saccule are demonstrate. affected in a certain way. The forces One of the best-known reflexes of of gravity and acceleration, caused by this sort is the postural righting reflex voluntary and involuntary motion, are of the cat. Since the pioneer work of also conveyed to the brain in the Magnus, ~2'13 this reflex has been form of impulses traveling along the studied under various conditions. If vestibular nerve. These impulses are a cat is first held in any other than all of the same intensity but they vary normal position and then dropped, the in frequency depending upon the di- animal immediately turns into the nor- rection and mode of acceleration. mal posture so that it always lands on The weight or movement of an oto- its feet. A similar reaction occurs when lith distorts the cell or cells closest to the cat, lying on its back with its head it. Minimal stimulation occurs when held in an almost normal position, is the maculas are horizontal and the moved vertically downward. However, otoliths rest on the hair cells ; maximal this reflex does not seem to function stimulation is obtained when the oto- when the cat is moved upward. Adri- liths hang from the cells or, with nor- an's experiment on the cat has shown mal head position, when they are that .changes in head position were as- pushed upward. Now, in the weightless state, the otoliths are deprived of sociated with an alteration of the iln- their weight, too, and this should result pulse rate, which was caused either by in a minute change of the cell struc- the act of tilting or by the angle of ture. This then will bring forth an tilt as such. He found that pressure alteration of the impulse rate of the toward the macula did not increase vestibular nerve. the stimulus. This may account for the It is the opinion of many investiga- lack of postural righting reflex during tors that the fo.rce of gravity exerts movement in the upward direction. the most fundamental influence upon From a practical viewpoint the ques- our spatial orientation. ~,7,11,14 How- tion was asked how the righting reflex ever, there is no need for the organism of the cat would work during sub- to obtain a conscious knowledge of the gravity and zero-gravity. Would the direction and amount of gravity. The cat turn around when held upside basic need is for a mechanism that d.own or would it stay in this position ? adapts the body automatically to their Is there a time factor involved which effects. This is done by means of the so-called postural reflexes which are may indicate adjustment and adapta- thought to serve to maintain or restore tion? How will other cues--for in- the "normal" position and posture of stance, visual orientation--affect the the body. This group of reflexes, functioning of the reflex? The an- which includes the static and statoklne- swers to these questions were sought tic reflexes of the body, reveals that not only to satisfy ottr own curiosity, 346 AVIATION MEDICINE POSTURE REFLEX--GERATHEWOHL AND STALLINGS bu,t to clarify the role of the otolith an altitude of approximately 12,000 organ during weightlessness. feet. The pilot of the craft (H.D.S.) flew the ascending arc of the para- METHOD bola at full throttle and the descend- Eight cats were used in the ex- ing part with about 75 per cent rpm periment; all were healthy young ani- in order to obtain weightlessness for mals born in the School of Aviation about 25 to 35 seconds. A.bsolute Medicine cat and dog kennels, and weightlessness or zero-gravity oc- raised from three different litters. curred for only a few seconds during Four of the kittens were about three each of t:hese maneuvers due to the weeks old when used in the experi- small accelerative forces present. These ment; two of the kittens were about unavoidable accelerations were of an eight weeks, and two young cats were estimated magnitude of about 0.03 to about twelve weeks of age. The ex- 0.05 G. The weightless state was indi- periments were conducted as follows: cated and controlled by the convention- Each of the three sets of experi- al G-meter installed in all fighter type mental animals first was taken into aircraft. Before entering into the para- the School of Aviation Medicine film bo.la and during recovery from the studio and placed on a table. The ani- dive, accelerations .of 1.25 G were not mals were then lifted up individually to be exceeded because it was observed and held upside-down in a long du'ring the first flight that the cats stretched position. They were released were extremely sensitive to an increase unexpectedly and dropped from an of acceleration. Five or six parabolas altitude of about 20 inches. Wfien the were performed during each experi- three-week-old kittens were employed, mental flight. the table was covered with a rubber The small kittens were taken along pad. In some of these experiments in pairs and kept in a container until the animals were blindfolded to ex- the working altitude was reached. The clude visual orientation. The behavior older animals were used one at a time of the animals was recorded on film. and carried on the arm of the experi- This experiment was repeated several menter in the aircraft (Fig. 1). The times so that its result could be con- cats were turned upside-down and re- sidered conclusive. leased after periods of 1, 51 10, 15, 20 The animals were then taken into and 25 seconds after entering the the air and exposed to short periods of weightless state. The behavior of the weightlessness. Virtual weightless- animals was studied under 'both blind- ness, or a state of reduced gravity, fold and nonblindfold conditions and was produced by flying a jet type air- recorded on film. craft (T-33 or F-94) along a Kep- Motion pictures were made using lerian trajectory. 4'5 The ascent to a 16 ram. Filmo camera, model 70 H, 20,000 feet was made at a rate of with a 13 mm. lens, f ~ 1.5, and a climb of 2,000 feet per minute. T'he film speed of 24 frames per second. cabin pressure at that altitude was Kodachrome film with a Kodak No. about 9.5 psi, which is equivalent of 83 filter, and one Eastman Panchro- Aucus~ 1957 347 POSTURE REFLEX--GERATHEWOI-'fL AND STALLINGS Fig. 1. Photograph of Fig. 2. Prompt ,righting Fig. 3. Delayed reflex: cat before the experiment reflex of cat immediately the cat turns slowly after a in the T-33 aircraft. upon entering the weightless certain delay. condition. 9 [8 AVIATION MFA}ICINE POSTURE REFLEX--GERATHEWOFITL AND STALLINGS Fig. 4. Postural righting Fig. 5. Disturbed reflex Fig. 6. No righting re- reflex fails completely; the associated with slight tum- flex. The animal floats cat floats in an inverted bling.

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